In the press section of a web-forming machine lots of water is rapidly removed from the web. The press section has usually one or two press nips and press felts are also used. The press nip is often formed of two rolls arranged to be loaded against each other.
The quick removing of water causes surface densification of the same side of the web where the water is removed. Simultaneously, an oil absorption reduction appears and the print quality degrades. To avoid these problems a smoothing press is arranged after the press section. Traditionally the smoothing press includes two rolls forming a nip. The web is thus pressed in the nip without any press felt. Due to this fact water is not removed from the web in the smoothing press. However, both surfaces of the wet web get smoother which improves drying of the web in the drying section.
One target in the web-forming is to maintain both sides of the web as symmetrical as possible. However, this has occasionally required very complicated structures in the press sections and smoothing presses. Also, when heating the paper or board some problems have occurred. In the conventional short heated smoothing nip the water may turn to steam with a sudden heat or press impulse. This leads to delamination of the web. Furthermore the brightness and opacity of the web may decrease and the web can stick to the surfaces, for example to the surface of the roll.